This invention relates to a filter insert for filtering the fresh air for the interior of a vehicle. Filter inserts of this type are normally made of an accordion-folded filter material, such as paper or a nonwoven.
These filter inserts are used, for example, in vehicle air-conditioning systems as well as in simple ventilating systems for vehicles. When dimensioning these filter inserts, it should be taken into account that the number of folds and the depth of the folds are functions of the required air flow rate and of the filter-technological characteristics. In this case, the pressure drop generated by the dust filter should be as minimal as possible.
During manufacturing, the filter insert is shaped first, in which case the pockets formed by the accordion folds are normally glued on the outer edges to a firm additional material. Then the individual folds, which were formed in this manner, are fixed at a distance from one another and the filter insert is inserted in a frame. By means of flexible polyurethane foam, the lower boundary edges of the filter insert are now connected with one another so that the distance of the individual folds is locked. This polyurethane foam is used simultaneously as a frame and as a sealing in order to later achieve a leakage-free connection of the filter inserted into a corresponding housing.
Some of the manufactured filter inserts do not have sufficient inherent stability and require a correspondingly expensive receiving frame for the installation. Another disadvantage concerns the recycling of the filter inserts, since additional materials, such as the polyurethane frame, must be disposed of in addition to the filter medium.
Furthermore, several working cycles are required for the known-manufacturing processes, for example, the gluing of the front edges, and the foaming or injection molding of the frame. It is also a disadvantage that the liquid sealing mass on the outer edges of the folds expands and reacts in the mold; that is, it flows also into the area under the actual fold pack and, as a result, partially closes the inflow or outflow opening so that the fold pack is not optimized with respect to the effective filter surface.
German Patent Document DE-OS 40 02 078 describes a filter insert which is made of a nonwoven that can be thermally bonded and in which the outer edge of the fold is bent and is welded by ultrasonics. However, the ultrasonic welding of such filter inserts has the disadvantage that expensive tools are required and this ultrasonic welding works reliably only in the case of a nonwoven which is made of a thermoplastic material. In the case of cellulose-containing filter materials, this process cannot be used in an optimal manner.